Optical data processing techniques can be used to encode and to decode or display composite images. For example, two or more images have been stored on a photographic plate with each image encoded by sequentially recording established transparencies of each image on fresh film. In so doing, a Ronchi grating can be used in two or more angular positions between a white light source and the transparency for encoding the photographic film. Thus a first recording may be exposed with the transparency at a reference 0 degree Ronchi grating position and a second recording may be exposed at a 90 degree Ronchi grating position. A multiplexed spatially encoded transparency can be obtained in this manner. For display, these images can be separated in the Fourier transform plane by placing a spatial filter in the plane which allows only the required spatial frequencies to be transmitted.
The traditional stereoprojection system uses a stereo camera and a stereoprojector. A pair of cameras may be held at a fixed separation and used to take stereoscopic pictures of an object or scene, the cameras shutters being operated simultaneously. When the prints or transparencies produced are viewed by the two eyes of an observer, a solid or three dimensional reproduction of the original scene is generated. By using a stereoprojector the two images of the scene are projected in polarized light onto a non-depolarizing screen, the vectors of polarization being at right angles in the two pictures while the viewing individuals are equipped with differently oriented polarizing filters so that the correct picture reaches each eye. A typical stereoprojection system is shown in FIG. 1 and comprises two independent systems 10 and 12 which are adjacent for projecting respective images to a screen 14. System 10 comprises a light source S.sub.1, condenser C.sub.1, a stereoscopic transparency of an input scene or object O.sub.1, projection lens L.sub.1 and a polarizer N.sub.1 for projecting a polarized image of O.sub.1 onto screen 14 from an acute angle with respect to system 12. System 12 is identical to system 10 and component parts are noted by the subscript 2 on the drawing. Polarizer N.sub.1 is perpendicular to N.sub.2 and images O.sub.1.sup.' and O.sub.2.sup.' are polarized images of the transparencies O.sub.1 and O.sub.2. Two cameras and two projectors are required in this system.
Prior art image regeneration is well established in the art and is also taught by Yu et al in Optics Communication, Volume 34, Number 1, July 1980, pages 11-14 and includes multi-image regeneration by superimposing a signal transparency with a highly efficient diffraction grating in the input plane of a white light optical processor. Typical of prior art encoding teachings is that of Chao et al in Optics Letters, Volume 5, Numbers 6, June 1980, pages 230-232. In Chao, a negative transparency of the object is available and is placed between a Ronchi grating and a fresh photographic film. The encoding is recorded on the new film. Subsequently a positive transparency of the object is processed in the same way with a different angular position of the grating, resulting in a multiplex spatially encoded transparency that is contrast-reversal.
As is not show, two separate television cameras may view the input scene to generate a stereo pair of images. However, since only a relatively small angle is necessary between viewing positions to create a stereoscopic or three dimensional image, for stationary or relatively slow moving focal objects such as a tank or crane, only one camera may be used. This is accomplished by angularly moving the camera within a plane between the shots, as for example back and forth with 64 millimeters between points where camera exposure of the film occurs. While two cameras and two films (or more) can be used, if only one film and one projector is used, the system is more simple, economical, and the need for characteristic matching of components is unnecessary. Once the photographic transparencies of the object are obtained they are processed as shown in FIG. 2 wherein a first transparency 20A is passed between a Ronchi grating 22A set at a reference 0 degree position and new photographic film 24A. Collimated white light is applied and the Ronchi grating is superimposed on the image to generate a series of dark lines on the pictures transferred to the new film. Subsequently either the grating 22A is rotated 90 degrees from the reference position or otherwise replaced by a grating 22B as shown and the film is advanced to the next frame 20B where new film frame 24 B is similarly encoded at a right angle to the first film.